Robot entertainment recently announced that players who own the original Orcs Must Die! on Steam will be able to unlock a special Classic Mode in Orcs Must Die! 2.
The special Classic Mode will include 10 Co-op maps from the original Orcs Must Die! and for those who don't own the original, it is now available on steam at 50% off.

See Classic Mode Screenshots below! (Clicking on an image triggers the gallery for easier viewing).